Impact of a National Immunisation Program on herpes zoster incidence in Australia

Summary Objectives To evaluate the impact of the National Herpes Zoster (zoster) Immunisation Program in Australia on zoster incidence. Methods Ecological analysis of zoster incidence related to timing of implementation of the national program in vaccine-targeted (70-79 years) and non-targeted age groups (60-69 and 80-89 years) during January 2013-December 2018 was estimated using interrupted time-series analyses. Results Prior to program commencement (Jan 2013 to Oct 2016) in patients aged 60-69, 70-79 and 80-89 years, incidence was mostly stable averaging respectively 7.2, 9.6 and 10.8 per 1000 person-years. In the two years following program commencement, incidence fell steadily in those aged 70-79 years, with an estimated decrease of 2.25 (95% CI: 1.34, 3.17) per 1000 person-years per year, with women having a greater decrease than men (2.83 versus 1.68, p-interaction<0.01). In the two non-vaccine-program-targeted age groups there was no evidence of reduction in zoster incidence: 60-69 years, 0.46 (95% CI: -0.46, 1.38) and 80-89 years, 0.11 (95% CI: -1.64, 1.87). Conclusions Two years after implementation, an estimated 7000 zoster cases were prevented through the national program. With known waning vaccine efficacy, continued surveillance is needed to ensure these early reductions in incidence are sustained.